The invention relates to an adjusting screw, notably to a screw for adjusting the inertia of a balance of a clockwork oscillator. It also relates to a clockwork balance comprising at least one such adjusting screw. The invention finally relates to a clockwork movement or to a timepiece, notably a watch, comprising such a balance or such an adjusting screw.
A balance the moment of inertia of which can be adjusted using adjusting screws arranged at its periphery is known. This type of device is notably known in its use within mechanical oscillators of which the basic frequency of the oscillator is adjusted through the moment of inertia of the balance. In general, such a balance comprises a felloe, arms and a certain arrangement of screws or balance weights fixed to the felloe of the balance and which, by adjusting their positions, can be used to alter the moment of inertia of the balance. These elements might have different masses so as to allow fairly fine adjustment of the running of the clockwork movement. These screws or balance weights are positioned using keys or screwdrivers that allow their position to be adjusted. These tools are generally provided with means that provide an indication of the screwing-in or the backing-off of the screw or of the balance weight with respect to the balance felloe. However, once this operation has been performed, it is no longer possible to determine the position of the balance weights.
Patent CH196706 relates to a variable-inertia balance which is provided with adjusting screws which are screwed from the outside of the balance felloe, making for easier adjustment and minimizing the risk of marking the balance felloe. This balance is one wherein the felloe has recesses to house the screw heads. Thus, the screw heads can easily be turned and do not project out from the felloe. However, the recesses made in the felloe carry the risk of having a negative interaction with any balance stop spring that might come into contact with the balance felloe.
Patent CH264669 relates to a balance provided with headless adjusting screws which are screwed from the outside of the balance felloe and sunk into the thickness thereof. This embodiment seeks advantageously to replace balances equipped with screws with heads that either protrude from the periphery of the felloe or are housed in a recess in the felloe.
Patent EP1837719B1 discloses a balance felloe comprising spurs of materials directed radially towards the inside of the balance, through each of which there passes a tapped hole to accommodate balance weights which are screwed in from the inside of the balance. In this configuration, it is awkward to grasp hold of the balance weights and there is a risk that the balance felloe will thus become marked during adjustment.